Horizons and assemblages of Middle Triassic Marine reptiles from Panxian, Guizhou, China

The Triassic marine reptiles from Guizhou Province, China,have attracted much attention during the past decade. The Triassic of Guizhou has traditionally yielded marine reptile fossils (Young 1958, 1960, 1965), including the Ladinian (Middle Triassic) locality in Dingxiao (Xingyi) that is famous for the pachypleurosaur Keichousaurus. However,the recent boom was fueled by the discovery of two new localities yielding well articulated specimens of various marine reptile groups (Wang et al., 2001; Jiang, Motani, Li, et al., 2005). The first to be reported was the locality near Xinpu in Guanling County (Li, 1999; Liu,1999), where the Wayao Member of the Falang Formation is exposed. The Wayao Member, which yields articulated marine reptile fossils, is now correlated to the early Carnian (Upper Triassic) based on conodonts, cephalopods, and ichthyoliths. However, some workers maintain that it corresponds to the late Ladinian (Middle Triassic) based on bivalves (see Jiang, Motani, Li, et al. 2005 and references therein). The second locality, near Yangjuan Village, Xinmin District, Panxian County appeared in publication slightly later (Wang et al., 2001. This locality yields fossils that are much older than those from Guanling or Dingxiao: a study of conodont biostratigraphy by Sun et al. (2006) established that the Upper Member of the Guanling Formation that is exposed in the area corresponded to the Anisian (Bithinian to Illyrian).